Rotary tablet presses are generally known and are widely employed in the pharmaceutical industry. They have a rotor which usually is driven about a vertical axis of rotation, and upper and lower rams, dies, a die-plate and cam systems, and at least one compressing station. While the rotor rotates the cam system provides for the upper ram and lower ram to be positioned vertically on the graduated circle. The dies are filled with powdered material requiring compression by means of appropriate charging systems, e.g. an agitator blade device or a filling shoe by which the dies are continuously charged while the rotor rotates. Furthermore, the graduated circle of the rotor has disposed thereon preliminary and main pressure rollers by means of which the material requiring compression is compacted into a tablet. The tablets are ejected from the dies by means of the associated lower ram which is actuated by an ejector cam.
The tablets have to meet quality criteria. For example, they include the weight, hardness, break resistance, tablet height, active-substance content, active-substance release, dispersal, friability, porosity, surface, moisture content, etc. It is known to perform quality surveillance in a way that random sampling is done from the tablets produced. They are tested at a laboratory, using appropriate testing instruments. The manual effort and also time consumption is large. A major period of time will pass until process corrections are possibly made. When made by conventional measuring procedures (HPCL procedures), measurements of the quantitative fractions of active substances and additives will take hours or even days.
It also has been known already to carry out a so-called online process control. A suitable testing instrument is placed in the very vicinity of the tabletting machine. Random samples are taken automatically from the flow of tablets, are supplied to the testing instrument, are singularized and measured. This allows to automatically make an intervention in the process from the testing instrument to a machine computer via a computer interface. This procedure, which also helps test only a fraction of the tablets produced, only permits to check a few quality parameters, e.g. the weight, break resistance, and height. Another known procedure utilizes a measurement of the compression force for each individual tablet in the tablet press to check quality criteria. As is known the compression force is a measure for the tendency to fracture, tablet weight, and tablet hardness. A check of each tablet produced is possible here. However, a drawback is that this involves the use of an indirect measuring procedure which does not met with a full acceptance in the preparation prescriptions of the pharmaceutical industry. It does not detect important quality parameters such as the active-substance identity, active-substance content, dispersal, porosity, content of additives, etc.